[PUGACHEV]

You have a 600 ton counterweight at the end of an 800 ton ribbon stretching 100,000 km above the Earth's surface: if you knew how to do the math, you could determine how much the structure's angular momentum would slow the Earth's rotation. Okay, I guess it wouldn't be much, but it would be something.

[glorgau]

you could determine how much the structure's angular momentum would slow the Earth's rotation.

Just as a wild guesstimate, I'd say it would be far less than the effect the moon has on the Earth's rotation. Yes, the Earth's rotation is slowing down, and the moon is moving farther away.